One of the big stories to hit the science blogosphere last week was about Rom Houben, a man who reportedly was (erroneously) believed by his physicians to be in a coma for 23 years after an accident whereas in reality he was conscious all along but paralyzed and unable to communicate this fact to the outside world.

As reported, the fact of his consciousness was only recently discovered with advanced brain scanning techniques not available to physicians at the time of his accident in 1983.

Some follow-up stories have raised the question about the accuracy of the details of his account, especially because it uses “facilitated communication”. James Randi raises similar concerns.

But leaving aside the debate over that particular question, I’d like to pose a broader mixed question about scientific testing for consciousness.

From a scientific and medical standpoint, it would clearly be valuable to know if there were a specific test that could determine if a person was truly comatose vs. “conscious but unable to communicate”. In other words, it would be extremely valuable to be able to test a seemingly comatose patient and determine whether there was “anybody home”, or there were only the bodily shell of what used to be a person.

It’s certainly plausible that some sort of scientific test might currently (or some day in the future) answer that question. But I’m not asking whether or not some particular current brain scanning technology actually answers this question.

Instead, suppose that some day a neuroscientist claims, “I’ve invented a machine that will reliably predict the presence or absence of consciousness. If such-and-such pattern of brain activity is present, then the patient is conscious. If that pattern is not present, then the patient is not conscious.”

My questions are as follows:

1) Would it be possible for a scientist to ever prove such a claim?

After all, consciousness is a subjective phenomenon that one experiences “from the inside”. In contrast, scientists can detect and measure brain activities which may be correlated with consciousness (such as a certain pattern of firing of neurons or a certain pattern of metabolic activity within the brain), but that’s that the same as detecting consciousness.

There are some schools of modern philosophical thought which claim that consciousness is equivalent to (and nothing more than) a specific type of brain activity. If one believes that, then the answer would presumably be “yes”, and the question would become purely an issue of science.

But in contrast, if one believes that consciousness is not equivalent to a specific pattern of brain activity (although related to the actions of the human brain in a still-not-fully-understood fashion), then the issue becomes murkier, leading to my next two questions:

2) Would a rational philosophy have anything to say about what would or would not be possible for scientists to claim? And would philosophers be able to give guidance as to what would constitute a proper standard of proof?

3) Or would no such claim by the neuroscientist possible? In other words, would a scientist only be able to claim that he is measuring an objective process that is highly probable to be correlated with a subjective sensation of consciousness — and that’s all anyone can ever do?

Or more colloquially:

1) Can you know if someone is home?
2) Can you know that you know it?
3) Or can you never really know it?

I freely admit that I don’t know the answers to these questions. But I’d be interested in hearing from others who might be able to shed some light — either scientific or philosophical.